Generally, automated cartridge systems (ACS) provide a mechanism by which multiple users in a data processing system can have common access to multiple data storage subsystems, such as multiple volume cartridge (MVC) devices. In conventional MVC devices, transfer of data sets or files generated by remote user computer systems for storage on a particular cartridge is performed using a first-in-first-out (FIFO) placement of such data files, or volumes, on the cartridge based on the time a data file is created/transferred.
While processing is made easier, the problem with such FIFO arrangements relate to the inability to efficiently utilize the physical space on the cartridge whenever earlier stored data files expire before later stored data files. More specifically, when a data volume file is generated or transferred, the data file is tagged with a predetermined expiration time. As a result, as shown in FIG. 1(a), if five different tape data volumes TV1 through TV5 were transferred onto a first MVC 10 order of time of creation, and volumes TV2 and TV3 expire before TV4 and TV5, then unusable gaps between valid volume files occur in MVC 10 as shown in FIG. 1(b).
In order to provide some measure of recovery of such unusable gaps, known management arrangements automatically move all valid data volumes in a given MVC whenever the ratio of the amount of valid data to the total data capacity on a cartridge exceeds a predetermined threshold. Such an arrangement is illustrated in FIG. 2 where data volumes TV1, TV4, and TV5 are moved to a second MVC 12.
While moving valid data volumes does allow reclamation of unused space on the first MVC, such a solution is not fully satisfactory since there is no control to prevent the very same problem from immediately occurring again on one or both MVC 10 and 12. As a result, a need exists for an improved method for transferring or optimizing placement of data volume files onto a MVC which overcomes the inefficiencies of conventional FIFO arrangements.